Weld bonding is the process of applying structural bonding adhesive between the flanges, then resistance welding the panels together. Currently many OEMs use this process at the factory, but in the aftermarket field only Ford and Chyrsler (includes Dodge and Jeep) require the weld bonding process for replacement of their components. BMW uses weld bonding during the assembly of their vehicles, but for replacement of their weld-bonded panels they require rivet bonding. Modern STRSWs have specific settings for weld bonding. Just remember to shunt the first weld.
MIG brazing (MIG-B) is welding performed with a gas metal arc welder, called gas metal arc welding/GMAW, with a silicone-bronze welding wire and 100 percent argon gas. MIG-B is gold in color, and is not a fusion weld. Sometimes referred to as silicone-bronze welding (SBW), MIG-B is not used in the assembly process — OEMs use the laser brazing process. Generally, you will find laser brazing on the roof to uni-side flanges and on some rear body panel flanges, but most OEMs require bonding for replacement of laser brazing. Toyota, Honda, VW and Mercedes-Benz are a few OEMs that have replacement procedures that require MIG brazing in the rocker and quarter panel sectioning areas. MIG brazing will likely become more of a required procedure as new advanced steels are introduced and require a lower HAZ.
Proper welding technique and cleanliness is crucial when welding aluminum. Techniques that are a little sloppy in steel welding will destroy an aluminum weld. You must weld like a machine, and porosity is a main area of concern when welding aluminum. When welding steel, you can use the push/forehand or pull/backhand technique, but with aluminum, you must use the push/forehand technique, as this will allow the weld site to be continuously protected by the shielding gas. Steel MAG welding uses a two-step trigger process, where you press the trigger (step 1) and the machine welds, and then you release the trigger (step 2) and the welding stops. When welding aluminum, a four-step trigger is the preferred method and sometimes it is required. A four-step trigger process is needed or required, due to a cold start at the beginning of the weld and the crater at the end of the weld. A four-step works as follows:
Step 1 — Hot Start: Depress the trigger and the welder starts at 150 percent of the weld current. For example, it you are set for 100 amps, the welder will increase the current to 150 amps. This Hot Start is generally only required for a second or two.
Step 2 — Welding Current: After one to two seconds release the trigger and the current drops back to the original setting. This step is where the majority of your welding is performed. Remember your finger is not on the trigger, the machine will be welding, however.
Step 3 — Crater Fill: As you get to the end of the weld, you will depress the trigger again and hold it depressed. The machine will slightly increase the gas and lower the current. This will do two things: clean the area and fill the crater that will form due to the amount of heat. This step is generally only need for two to three seconds.
Step 4 — Weld Stop: After two to three seconds, release the trigger and the weld current is cut off and the gas will stay on and flow for two to three seconds to cool the area.
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